The invention relates to measurement and control of fluid conditions, and more particularly, to measurement and control of solids suspended in a liquid.
In many industrial processes and applications it is important to measure and control the concentration of solids that are suspended in a liquid. The concentration of solids suspended in a liquid is typically determined by optically measuring the amount of light that can pass through the liquid. As the concentration of suspended solids increases, the amount of light able to pass through the liquid consequently decreases. A well-known model known as the Lambert-Beer Law describes this relationship between concentration of solids suspended in a liquid and corresponding light transmission through the liquid.
Unfortunately, many industrial monitoring applications involving liquids pose difficult challenges to optical measurement of suspended solids concentration. For instance, many cases involve the presence of gas bubbles, including entrained air, in a test sample. The presence of gas bubbles, including air bubbles, increases scattering and absorption of light within a liquid sample, which causes measurements to falsely indicate a higher suspended solids concentration than is actually present in the liquid sample.
Typically with optical measurements, a stilling well has been used to minimize errors in the measurement of suspended solids concentration caused by gas bubbles. A stilling well provides an isolated region that allows entrained gas to separate before a suspended solids concentration measurement is made. Unfortunately, this technique of using stilling wells tends to introduce other measurement errors and increases maintenance requirements. For instance, as the entrained gas separates from the liquid sample in the stilling well, many suspended solids can also separate from the liquid sample thereby reducing measurement values of suspended solids concentration below their actual value. Also, the settled solids can accumulate and plug associated sensors, screens, and pipes (referred to as xe2x80x9clinesxe2x80x9d) that carry the sample fluids, thereby increasing maintenance requirements.
Apart from the issues involving a stilling well, optical measurement of suspended solids concentration has additional difficulties. Sample fluid lines tend to plug due to an accumulation of solids. Optical measurement systems usually employ sample windows to allow light from a light source to pass from an exterior side of the sample fluid line through the sample fluid to be received on the opposite exterior side of the sample fluid line. During operation, the sample windows tend to become scaled and coated with material that absorbs and scatters light, thereby decreasing light transmission and falsely increasing values for measured suspended solids. Attempts have been made to keep sample fluid lines and sample windows clear, however, these attempts have proved to be ineffective or too expensive, complicated and labor-intensive.
The present invention resides in a system for measuring suspended solids in a sample liquid. The system comprises a pressure chamber configured to receive the sample liquid therein and operable to apply an increased pressure to the received sample liquid sufficient to reduce at least a portion of the entrained gas of the received sample liquid. The system further includes a sensor configured to generate a signal based upon an amount of suspended solids in the received sample liquid after the pressure chamber applies the increased pressure to the received sample liquid. The system further includes a controller coupled to the sensor. The controller is configured to control an amount of chemical released into a liquid containing suspended solids based upon the signal generated by the sensor.
In a disclosed embodiment of the system for measuring suspended solids in a liquid with entrained gas, the system includes a measurement chamber with a sealable opening to receive a sample of the liquid. The measurement chamber is selectively changeable in volume with the sample liquid therein between a first configuration with an internal first volume and a second configuration with an internal second volume. The second volume is smaller than the first volume such that when the measurement chambers change from the first configuration to the second configuration with the sample liquid therein, an increased pressure is applied to the liquid sample sufficient to dissolve at least a portion of the entrained gas into the sample liquid. The system further includes a detector positioned to detect the concentration of the suspended solids in the sample liquid in the measurement chamber when in the second configuration with the increased pressure applied to the sample.
In the disclosed embodiment the detector comprises a light source and a light detector. The light source is configured to emit light and is positioned with respect to the measurement chamber to direct the emitted light into the measurement chamber when in the second configuration and through the pressurized liquid sample therein. The light detector is positioned with respect to the measurement chamber to generate a signal based upon the light received that was directed by the light source into the measurement chamber and through the pressurized liquid sample therein when the measurement chamber is in the second configuration. In the disclosed embodiment the measurement chamber has first and second opposing wall portions that are transparent. The first and second opposing wall portions have external surfaces and the light source is positioned adjacent to the external surface of the first opposing wall portion and the light detector is positioned adjacent to the external surface of the second opposing wall portion. The light source is further positioned to direct light toward the first transparent opposing wall portion and the light detector is positioned to receive light through the second transparent opposing wall portion.
The disclosed embodiment of the system includes a piston having a head with a surface in part defining the internal volume of the measurement chamber. The piston is movable between first and second positions corresponding to the first and second configurations of the measurement chamber, respectively. When the piston is in the first position the piston surface defines a first volume and when the piston is in the second position the piston surface defines the second volume. In the disclosed embodiment, the opening of the measurement chamber is coupled to a valve having open and closed positions. When in the open position, the valve allows the sample liquid to enter and leave the measurement chamber. When in the closed position the valve prevents the sample liquid from exiting the measurement chamber.
The system further includes a controller electrically coupled to the detector. The controller is configured to meter amounts of chemicals being introduced into a liquid stream containing suspended solids from which the sample liquid received in the measurement chamber originates, the metering being in response to the concentration of the suspended solids detected by the detector.
In the disclosed embodiment, the system includes first and second cylinder arranged along a common longitudinal axis. A transparent cylinder liner is positioned within the second cylinder. A first end cap is coupled to a first end of the first cylinder, a second end cap is coupled to the second end of the first cylinder and to a first end of the second cylinder, and a third end cap is coupled to a second end of the second cylinder. The second end cap has an aperture therethrough providing a passageway between the interior volumes of the first and second cylinders. The third end cap has a fluid aperture therethrough providing a fluid passageway to the interior volume of the transparent cylinder liner. A fluid valve is coupled to the third end cap aperture for passage of fluid to and from the interior volume of the transparent cylinder liner. A piston shaft is slideably disposed within the second end cap aperture and has a first piston head attached to a first end thereof within the interior volume of the first cylinder, and a second piston head attached to a second end thereof within the interior volume of the transparent cylinder liner. A light source is positioned to direct light through a first measurement port of the second cylinder and a light detector is positioned with respect to the second cylinder to receive light from the light source directed through a second measurement port of the second cylinder. The light detector is configured to generate an electrical signal based upon the light received by the light detector.
The invention further includes a method for sampling a liquid containing suspended solids and entrained gas. The method includes transferring a sample of the liquid containing suspended solids and entrained gas to a measurement chamber, and applying pressure to the sample in the measurement chamber in an amount required to reduce the entrained gas in the sample. The method further includes measuring the suspended solids in the pressurized sample with the reduced entrained gas. In the disclosed embodiment, the method further includes screening the sample before transferring the sample to the measurement chamber using a screen, and back flushing the measurement chamber through the screen to clean the screen after measuring the suspended solids in each pressurized sample. Further, the method includes wiping the measurement chamber surfaces after measuring the suspended solids in each pressurized sample.
Other features and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings.